Those who quibble about the ftp being a separate entity from mail protocol would do well to look at RFC 524 from 1973. There, the MAIL command is implemented within the ftp structure (that is, it is an ftp command).
I've found it interesting that 524 never addresses the matter of data representation: (7 bit ASCII PDP-10), (8-bit IBM EBCDIC), (6-bit Univac Fieldata), (9-bit MULTICS), etc. This makes sense when viewed in the light of RFC 354 (ftp), as 354 makes provision for non-7-bit ASCII codes. --Chuck